Neue Coleone und Royleanone aus Coleus somaliensis S. MOORE

Novel Coleons and Royleanones from Coleus somaliensis S. M_OORE Reexamination of the fraction of polar diterpenoids from the title plant, in addition to the previously identified compounds of Scheme 1 [2] [3], leads to the isolation of (15S)-coleon D ( 8 ), the abeo-royleanones 9–11 and the spirocoleons 12–17 . Crystalline (15S)-coleon I ( 3a ) is characterized.     

Interaction of NO and O2 with Pd(111) surfaces. I.

The adsorption of NO on Pd(111) was studied by means of LEED, UPS and thermal desorption measurements. Non-dissociative adsorption is characterized by additional maxima in the photomission spectra at 2.6, 9.2 and 14.6 eV below the Fermi level originating from chemisorption levels which are derived from the highest occupied molecular orbitais of NO. Thermal desorption takes place from three distinct states (α, β and γ) corresponding to binding energies of about 15, 17 and 31 kcal/mole, respectively, with about equal populations. The α-state is associated with a 2 × 2 LEED pattern and the β-state with a c4 × 2 structure, whereas the γ-state corresponds to disordered adsorption at low coverages. Plausible structure models are proposed for the ordered structures with θ = 0.75 for the α-state and θ = 0.5 for the β-state. The strong decrease of the adsorption energy is explained in terms of pronounced short-range repulsive interactions between neighbouring adsorbate molecules.     

Investigation of neutron-deficient isotopes in the barium-region

Bombarding targets of 106Cd,¹⁰⁸Cd and¹¹⁰Cd with¹⁶O ions of 52.5–66.0 MeV neutron deficient barium, cesium and xenon isotopes were produced and have been studied using excitation functions and neutron-gamma, proton-gamma, alpha-gamma and gammagamma coincidence measurements. Partial level schemes for¹²³Ba and¹²¹Ba were proposed. A number of gamma transitions was assigned to the different product nuclei. The measured particle emission probabilities from the compound nuclei are compared with different evaporation models. The models mostly underestimate neutron emission and often overestimate the emission of alpha particles.     

Dependency of the delocalized charge density and of the structural parameters on the pseudorotational parameter phi in 1,1-dicyanocyclopentane

Encouraged by the results we recently obtained from the exploration of the dependency of the structural parameters of 1,1-dichlorocyclopentane (J. Chem. Phys. A 2004, 108, 4658) on the pseudorotational parameter phi, we decided to reinvestigate the structure and the potential function governing the conformational equilibrium of 1,1-dicyanocyclopentane (DCCP) in the light of these novel results. The improved potential function we developed describes more adequately the dependency of the geometrical parameters on the pseudorotational phase angle phi. In the present work, we also incorporated additional terms into the equations we developed earlier (J. Chem. Phys. A 2004, 108, 4658; J. Mol. Struct. 2002, 612, 181) for describing the dependency of the distribution of the delocalized net charges throughout the ring on phi to account for the observed systematic deviations between the computed atomic distances and those provided by these equations. Although the overall fit of the electron diffraction was not significantly different from that which we presented previously, however, applying these extended equations has led to a better fit by refining a smaller number of parameters.     

Interaction of NO and O2 with Pd(111) surfaces. II

At least three different types of oxygen atoms may be present in the surface region of Pd(111) which may be distinguished by their thermal, chemical, structural and electronic properties. Exposure to O₂ at low temperatures causes the formation of 2 × 2 and $\text{3}\text{×}\text{3}\text{R30°}$ structures from chemisorbed oxygen, the latter being probably stabilized by small amounts of H_ab or CO_ab on the surface. The initial sticking coefficient was estimated to be about s₀ ≈ 0.3, the adsorption energy ~55 kcal/mole. The photoelectron spectrum exhibits an additional maximum at 5 eV below E_F. During thermal desorption dissolution of oxygen in the bulk strongly competes; on the other hand absorbed oxygen may diffuse to the surface giving rise to high temperature peaks in the flash desorption spectra. High temperature (~1000 K) treatment of the sample with O₂ causes the formation of a more tightly bound surface species also characterized by a 2 × 2 LEED pattern which is chemically rather stable and which is considered to be a transition state to PdO. The latter compound is only formed by interaction with NO at about 1000 K via the reaction $\text{Pd}\text{+}\text{NO}\text{→}\text{PdO}\text{+}\text{1}\text{2N}{}_2$ which offers a rather high “virtual” oxygen pressure. This reaction leads to drastic changes of the photoelectron spectrum and is also identified within the LEED pattern.     

Photoproduction of negative pions on a polarized neutron target in the resonance region

At the Bonn 2.5 GeV electron synchrotron the first measurements of the target asymmetry for the reaction γ + n ↑ → π^? + p have been performed. The negative pions were detected in a magnetic spectrometer at a constant pion c.m. angle of 40° and photon energies between 0.45 GeV and 2.0 GeV. Deuterated butanol was used as target material. The polarization of the deuterons was about 16%. The results show a significant difference from the previously measured π⁺ asymmetry.